[Core] Use GetAPInt instead of constructing APInts in place
[Core] Use GetAPInt instead of constructing APInts in place

GetAPInt should be able to handle all cases. I have plans to generalize
the float dumping logic and this makes it easier to do later.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@370255 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb